1. Field of the Invention
The present invention relates to a vehicle brake fluid pressure control apparatus which includes as a pressure regulator valve a normally open electromagnetic valve which can change arbitrarily a valve closing force (a valve opening force) in accordance with the amount of energization.
2. Description of the Related Art
Conventionally, there have been known vehicle brake fluid pressure control apparatuses which include pumps for pressurizing fluid in wheel brakes so as to increase brake fluid pressures therein and pressure regulator valves for regulating the brake fluid pressures in the wheel brakes (refer to JP-A-2001-260840, for example). In this technique, used as the pressure regulator valve is a proportional electromagnetic valve (liner solenoid valve) which generates a valve closing force which is proportional to the magnitude of an electric current given. With this proportional electromagnetic valve, a differential pressure between an upstream side and a downstream side of the pressure regulator valve can be changed in proportion to a change in valve closing force (that is, a change in the magnitude of electric current).
An electric current given to the pressure regulator valve is controlled based on a map stored in advance, whereby the brake fluid pressures in the wheel brakes can be controlled well.
Incidentally, in such proportional electromagnetic valves, there may be a proportional electromagnetic valve in which depending on the construction thereof, an output current value for opening the valve from a closed state differs from an output current value for closing the valve from an open state (a valve closing property differs from a valve opening property). In the event that the valve opening output current value differs from the valve closing output current value, two different maps, a valve closing map and a valve opening map, are prepared as maps so that the current control is performed by referring to only the valve closing map when performing a valve closing control, while when performing a valve opening control, the current control is performed by referring to only the valve opening map.
In the event that the valve closing property differs largely from the valve opening property, however, in opening the valve from the closed state, there has been a fear that an actual fluid pressure reduction amount becomes larger than a target value or a fluid pressure reduction gradient deviates from a target fluid pressure reduction gradient only by switching the maps directly from the valve closing map to the valve opening map for reference.